[ovs-dev] [PATCH] netlink: make Netlink socket receive buffer 4x larger

Ben Pfaff blp at ovn.org
Mon Mar 29 23:20:53 UTC 2021

On Mon, Mar 29, 2021 at 05:26:34PM -0500, Ansis Atteka wrote:
> Under high load I observed that Netlink buffer constantly
> fills up for daemons querying Conntrack Table that has a
> lot of entries in it:
> netlink_notifier|WARN|netlink receive buffer overflowed
> This patch mitigates the problem by increasing socket
> receive buffer size.  Ideally we should try to calculate
> buffer size required, but it would be more sophisticated
> solution than simply increasing buffer size.
> Signed-off-by: Ansis Atteka <aatteka at ovn.org>
> VMware-BZ: #2724821

Are you sure that it's queries that cause overflows?  Queries retrieve
individual records, which would not overflow the 1 MB receive buffer
that was used before.  Dumps can retrieve large numbers of records, but
the kernel works in a way such that the records aren't all written in
one go but gradually as userspace reads them.

Usually, the cause of an overflow is because there's a Netlink socket
that's subscribed to receive updates from some particular subsystem
(I guess that's conntrack in this case).  Those do arrive asynchronously
and can overflow if they arrive faster than userspace can retrieve and
process them.

I can believe that that is the problem here.  Is it?  If so then
probably the solution is right, but the description of the problem is
slightly wrong.

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